1. Field of the Invention
The present invention relates to an adsorbent and a canister.
2. Description of the Related Art
Liquid fuel such as gasoline or light oil is used as fuel in most of automotive vehicles utilizing motive power generated by combustion engines. Since the liquid fuel contains volatile organic compounds (hereinafter referred to as VOCs), volatilization of VOCs in a fuel tank occurs over a nonoperational period during which the combustion engine stays stopped. Vaporization of VOC can increase an internal pressure of the fuel tank.
In an automobile having an internal combustion engine, vaporized VOCs are collected in a canister which includes an adsorbent in a closed container. Specifically, during the nonoperational period, the interior of the container is connected to the headspace of the fuel tank in order to allow the adsorbent made of activated carbon to adsorb the vaporized VOC. It should be noted that when activated carbon adsorbs VOCs, its adsorbability is lowered in accordance with an amount of adsorption. For this reason, in an automobile equipped with a canister, air is made flow through the adsorbent layer as a purge gas in an operational period during which an internal engine is in operation so as to cause desorption of VOCs from the activated carbon. Note that the gas discharged from the canister is burned in the internal combustion engine.
A canister requires that a sufficient amount of VOCs is adsorbed by activated carbon during the nonoperational period and a large proportion of adsorbed VOCs is desorbed from the activated carbon during the operational period. Although sufficient VOC adsorption and desorption amounts are achieved when activated carbon prepared by the methods described in Jpn. Pat. Appln. KOKAI Publication No. 2-175608, Jpn. Pat. Appln. KOKAI Publication No. 6-100311, Jpn. Pat. Appln. KOKAI Publication No. 7-277716 and Jpn. Pat. Appln. KOKAI Publication No. 8-169706 is used, a canister is required to further increase the VOC adsorption and desorption amounts. In addition, the methods described in the documents require a long period of time for activation treatment to obtain activated carbon.